In the field of magnetic recording such as a hard disc, recording density is currently exceeding 400 Gbit/inch2 in area density due to the increases in properties of storage media, recording heads, and reproducing heads, and the recording density is going to further increase.
Among them, a magnetic storage medium used in a current hard disc has a problem of heat fluctuation. It is known that as recording density further increases, it becomes difficult to stably store magnetic information for a long time.
The problem of heat fluctuation is represented by a relation between (i) a magnetic anisotropic energy vKu that is a product of volume v of magnetic particles forming magnetic bits of a magnetic storage medium and a magnetic anisotropic energy constant Ku and (ii) thermal energy kT (k: Boltzmann's constant, T: temperature). It is known that when the magnetic anisotropic energy vKu gets so small as to be approximately several ten times larger than the thermal energy kT, magnetic information is lost notably due to heat fluctuation.
As one means for solving the problem of heat fluctuation, there is proposed a magnetic storage medium called patterned media (see Patent Documents 1-3 for example).
The magnetic storage medium called patterned media is a medium in which one magnetic particle forms one magnetic bit and a non-magnetic material exists between magnetic particles to separate them, as opposed to a magnetic storage medium (granular medium) employed in a conventional hard disc that is designed such that a plurality of small magnetic particles form one magnetic bit. The magnetic medium called patterned media is highly effective in solving the problem of heat fluctuation, since the magnetic medium allows a larger volume v of magnetic particles than the granular medium.
On the other hand, since one magnetic particle forms one magnetic bit, variations in the size of individual magnetic particles and in the array period of individual magnetic particles causes variations in a magnetic field required in recording and noises in reproduction. Therefore, it is necessary to make an array period pattern of magnetic bits as even as possible.
As a technique for realizing such patterned media, Patent Document 1 discloses a magnetic storage medium that can be produced with use of a block copolymer.
Further, Patent Document 2 discloses a magnetic storage medium where fillers made of a hard magnetic material fill alumina nano holes obtained by processing alumina.
Further, Patent Document 3 discloses a magnetic storage medium including a recording magnetic layer that includes a plurality of magnetic columns made of a magnetic material and a non-magnetic region that is made of a non-magnetic material and that exists between the magnetic columns.
Patent Document 3 describes that material particles used as making for forming patterned media are prepared by depositing and growing a predetermined material to have an island-shape through sputtering using a predetermined target. Further, Patent Document 3 describes that Ag, Cr, W, Mo, Ta or alloys thereof may be used as a material for forming the material particles (see paragraph [0038] of Patent Document 3).
Further, Patent Document 3 describes another masking that is obtained in such a manner that a solution in which a compound that can be deposited as so-called nano particles are dissolved is applied on the surface of a magnetic material film through spin coating and then a liquid component of the solution is evaporated to deposit the nano particles (see paragraph [0040] of Patent Document 3).
Other than the methods disclosed in Patent Documents 1-3, there are known methods such as: a method for applying a resist material on a magnetic material, forming a pattern with use of photolithography or electron beam exposure, developing the pattern, and thereafter etching the magnetic material with use of the resist material as masking so as to produce patterned media; and a method for directly processing a magnetic material with use of FIB (Focused Ion Beam) and patterning the magnetic material.
However, the conventional methods have a problem that it is difficult to form highly uniformed magnetic particles with a periodic pattern through a simple process at a time.
Specifically, each of the methods disclosed in Patent Documents 1 and 2, the method using nano particles that is disclosed in paragraph [0040] of Patent Document 3, and the well-known methods other than the methods disclosed in Patent Documents 1-3 for processing a magnetic material with use of photolithography, electron beam lithography, and FIB requires a large number of devices and steps that are not required in the production of the conventional granular medium, which results in higher production costs and more complex production steps.
Further, the aforementioned methods other than the method using FIB generally require a wet process, which may cause attachment of contaminated substances in a chemical solution and cause a defective product. In the method using FIB, direct processing causes chips and the chips attach as contaminated substances.
Further, among the aforementioned well-known methods, the methods using photolithography, electron beam lithography, and FIB require serially forming individual patterns one by one, and consequently the production of a medium requires a longer time and higher costs.
On the other hand, in the method disclosed in paragraph [0038] of Patent Document 3 in which a predetermined material is deposited and grown to have an island-shape through sputtering, a pattern can be formed by film formation through sputtering. Therefore, it is considered that the method is compatible with conventional steps for producing a medium. However, the size and movement energy of individual particles ejected from a target through the sputtering vary, and consequently it is difficult to uniform the island-shape on a substrate in nano meter order. Further, the actually formed island-shape has random size and random period, and therefore a substrate having the shape formed through this method is difficult to be used as a pattern for the patterned media that requires high uniformity.
[Patent Document 1]    Japanese Unexamined Patent Publication No. Tokukai 2000-251236 (published on Sep. 14, 2000)
[Patent Document 2]    Japanese Unexamined Patent Publication No. Tokukai 2002-175621 (published on Jun. 21, 2002)
[Patent Document 3]    Japanese Unexamined Patent Publication No. Tokukai 2004-272997 (published on Sep. 30, 2004)